Chloroprene rubbers curing systems

The comparative estimation of efficiency of zinc oxide and ZnCFO similar concentrations (3,0 5,0 7,0 phr) as the agents of metaloxide vulcanization system was carried out on example of modelling unfilled elastomeric compositions from chloroprene rubber of recipe, phr chloroprene rubber - 100,0 magnesium oxide - 7,0. Kinetic curves of rubber mixes curing process at 155°C are shown on fig. 8. The analysis of the submitted data testifies, that at increase of zinc oxide contents vulcanization kinetics is changed as follows the scorch time and optimum cure time are decreased, the cure rate is increase. Vulcanization... 

The close structural similarities between poly chloroprene and the natural rubber molecule will be noted. However, whilst the methyl group activates the double bond in the polyisoprene molecule the chlorine atom has the opposite effect in polychloroprene. Thus the polymer is less liable to oxygen and ozone attack. At the same time the a-methylene groups are also deactivated so that accelerated sulphur vulcanisation is not a feasible proposition and alternative curing systems, often involving the pendant vinyl groups arising from 1,2-polymerisation modes, are necessary. 

Zinc oxide, which is formed from the burning of zinc metal, was the first nonblack filler nsed for reinforcement of rubber compounds. Although zinc oxide and magnesinm oxide are still used as reinforcing fillers in some specialty compoimds, particnlarly those that reqnire heat resistance, their role in rubber compoimding in the last several decades is that of an activator for the sulfur cure system or as curatives for chloroprene rubber compounds. 

Macaione et al [235] have used TG for the characterisation of SBR, BR and NR in mono-, di-, or triblend rubber systems and carbon-filled rubber composites and determined the percentage of highly volatile organics, elastomer(s), carbon-black, and inorganic residue for each sample. Lochmiiller et al [194] applied factor analytical methods to evaluate TG results of a series of rubber blends and mixtures composed of chloroprene rubber, NBR, and common rubber additives. TG and measurements of toluene extractable matter of cured siloxane rubbers thermally aged in inert gas atmosphere at 80° C showed a build-up of low-MW fragments in the rubber network with age [244]. 

Pre-cured bromobutyl material is a procured vulcanized bromobutyl rubber suitable for site lining and delivered with suitable adhesive system based on chlorobutyl, chloroprene and polyisocyanate. 

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